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POpassing pointer to int array into template function
 

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  1. POpassing pointer to int array into template function
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    <p>I have been stuck on this all afternoon, and even tried the following search: "c++ passing pointer to array via function", and can't find a working answer, so here is my question.</p> <p>Before I begin, please, this is NOT an OpenGL question, this is an array pointer passing question.</p> <p>Also, don't get '....' (4 dot) mixed up with '...' (3 dot). There is a lot of code I am skipping over with '....' (4 dot), the ... (3 dots) are the ellipse parameter for variable number of paramters passed to a function.</p> <p>These are the snippets from the four files involed:</p> <p>OpenGL.h</p> <pre><code>class OpenGL { .... (other unrelated stuff) public: int * iPixelFormatAttribList[]; &lt;---------- .... </code></pre> <p>utilities.h</p> <pre><code>template &lt;typename T&gt; void LoadArray (T * [], int, ...); &lt;-------- </code></pre> <p>utilities.cpp</p> <pre><code>// Dynamically Load Array. template &lt;typename T&gt; void LoadArray (T * Dest [], int count, ...) { &lt;------- va_list list; va_start(list,count); T * temp [] = new T [count]; for (int cnt = 0; cnt &lt; count; cnt++) * Dest[cnt] = va_arg(list, T); va_end(list); Dest = temp; delete [] temp; } </code></pre> <p>OpenGL.cpp</p> <pre><code>void OpenGL::V3_SetupPixelFormat() { ..... LoadArray ( iPixelFormatAttribList, 15, &lt;--------- WGL_DRAW_TO_WINDOW_ARB, GL_TRUE, WGL_SUPPORT_OPENGL_ARB, GL_TRUE, WGL_DOUBLE_BUFFER_ARB, GL_TRUE, WGL_PIXEL_TYPE_ARB, WGL_TYPE_RGBA_ARB, WGL_COLOR_BITS_ARB, 32, WGL_DEPTH_BITS_ARB, 24, WGL_STENCIL_BITS_ARB, 8, 0 // End of attributes list ); </code></pre> <p>Ok, So, here what I am trying to do. I know that in a class definition, (OpenGL.h, the OpenGL class), that space is not allocated for any members, and because when I create it, I do not know how many paramters I am going need for an array, I need to find a way to dynamically allocate and setup the list so I can pass it into later OpenGL calls.</p> <p>(Another reason I decided to setup a dynamic loading list like this was because there are several arrays involved like this, loading arrays, and I may also need this same type of functionality later with doubles and what not for vector data. Creating this utility template seems a forward thinking way to go.)</p> <p>This all <strong>LOOKS</strong> Ok, and in fact, it compiles clean, but it does not link. I get the following:</p> <pre><code>**** Internal Builder is used for build **** windres --use-temp-file -i..\res\resource.rc -o..\res\resource_rc.o g++ -D_SS_DEBUG_ -ID:\Dev\Projects\Eclipse\OpenGL3\res -O0 -g3 -Wall -c -fmessage-length=0 -std=gnu++0x -o src\OpenGL.o ..\src\OpenGL.cpp g++ -D_SS_DEBUG_ -ID:\Dev\Projects\Eclipse\OpenGL3\res -O0 -g3 -Wall -c -fmessage-length=0 -std=gnu++0x -o src\main.o ..\src\main.cpp g++ -D_SS_DEBUG_ -ID:\Dev\Projects\Eclipse\OpenGL3\res -O0 -g3 -Wall -c -fmessage-length=0 -std=gnu++0x -o src\Utilities.o ..\src\Utilities.cpp g++ -D_SS_DEBUG_ -ID:\Dev\Projects\Eclipse\OpenGL3\res -O0 -g3 -Wall -c -fmessage-length=0 -std=gnu++0x -o src\App.o ..\src\App.cpp g++ -D_SS_DEBUG_ -ID:\Dev\Projects\Eclipse\OpenGL3\res -O0 -g3 -Wall -c -fmessage-length=0 -std=gnu++0x -o src\Win.o ..\src\Win.cpp g++ -o OpenGL3.exe src\main.o src\Win.o src\Utilities.o src\OpenGL.o src\App.o ..\res\resource_rc.o -lopengl32 -lglew32 -lglu32 -lkernel32 -lgdi32 -lcomdlg32 -luser32 src\OpenGL.o: In function `ZN6OpenGL19V3_SetupPixelFormatEv': D:\Dev\Projects\Eclipse\OpenGL3\Debug/../src/OpenGL.cpp:54: undefined reference to `void LoadArray&lt;int&gt;(int**, int, ...)' collect2: ld returned 1 exit status Build error occurred, build is stopped Time consumed: 3000 ms. </code></pre> <p>The key line to me looks like: </p> <pre><code> undefined reference to `void LoadArray&lt;int&gt;(int**, int, ...)' </code></pre> <p>What this seems to tell is the way I am calling the function:</p> <pre><code>LoadArray ( iPixelFormatAttribList, 15, WGL_DRAW_TO_WINDOW_ARB, GL_TRUE, WGL_SUPPORT_OPENGL_ARB, GL_TRUE, .... </code></pre> <p>And the way I am defining the template function:</p> <pre><code> template &lt;typename T&gt; void LoadArray (T * [], int, ...); </code></pre> <p>and:</p> <pre><code> template &lt;typename T&gt; void LoadArray (T * Dest [], int count, ...) { </code></pre> <p>don't match. I get that much.</p> <p>What I don't get is how to adjust the template (Or the call) so that they match so it can link (i.e. I got my function signatures all screwed up.)</p> <p>The basic idea to this is, I call LoadArray with an array pointer, the element count, and the list of elements, and it modifies the pointer so that it points to a new list containing the array elements.</p> <p>I am sure there are fancy C++ ways to do this, but I want to understand how to make this work as it seems it should here. (i.e. it would help me to learn if I know what exactily I was doing wrong here, rather then a redirect solution that won't teach me what I did wrong, I know enough to know I am missing something in the syntax of passing an array pointer like this, I just can't figure out the right black magic to get it right.)</p> <p>Thanks.</p>
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